Where the silver in the denarius went
Between Septimius Severus and Aurelian, Roman silver coinage lost almost all its precious metal. This was no accident: it was a policy, pursued by emperors who had little choice.
A state that costs more
Septimius Severus raised the legionaries' pay; Caracalla raised it again. The army absorbed most of the imperial budget, and the wars of the period were simultaneous on several fronts. Faced with tax revenue that did not keep up, an emperor had three levers: raise more tax, confiscate, or strike more coins from the same quantity of metal.
The third lever is the least visible in the short term. It is the one that was used, reign after reign.
The mechanism
Debasement takes two forms. Either the weight of the coin is reduced, or its silver content is. The antoninianus created in 215 combined both: it weighed about one and a half denarii and was worth two, which amounts to creating a quarter of its value out of nothing.
Modern analyses, made by sampling the core of the flan and not the surface, show a continuous decline: of the order of 50 per cent silver under Septimius Severus, about 40 under Elagabalus, around 20 by the time of Gordian III, then collapse under Gallienus. Measuring at the surface distorts everything: silvering concentrates the silver on the outside of the flan.
What this changes for a collector
A so-called silver coin of 268 has little silver about it, and its condition depends on that: a billon flan corrodes like bronze, with green or brown patinas one would never see on a Severan denarius.
It also explains the prices. An antoninianus of Gallienus is abundant because it was struck in vast quantities and because it was never worth melting down. The denarii of the beginning of the period, by contrast, largely disappeared into the crucibles.
Further reading
K. W. Harl, Coinage in the Roman Economy, 300 B.C. to A.D. 700, Baltimore, 1996, the chapters on the third century.
J.-P. Callu, La politique monétaire des empereurs romains de 238 à 311, Paris, 1969: the standard work on the period, still debated but never replaced.
K. Butcher and M. Ponting, ‘The Denarius in the First Century’, and their later work on third-century alloys.